Rotifers of the Bdelloidea class are multicellular invertebrate organisms so small that they are usually only seen under a microscope. They are also highly resistant. They spend long periods in a state of suspended animation in dry, cold environments where very little food or oxygen is available. Led by biologist Stas Malavin from the Institute of Physicochemical and Biological Problems in Soil Science in Pushchino, Russia, a group of researchers successfully brought specimens of these organisms back to life after they had been frozen for more than 24,000 years. The samples were obtained from permanently frozen soil in Siberia. Once thawed, the rotifers reproduced (Current Biology, June 7). The researchers then selected 144 individuals from this new lineage, cooled them to minus 15 degrees Celsius, and brought them back to room temperature a week later. Some survived, suggesting they have mechanisms that protect their cells from extremely low temperatures.
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